Function findBestWaypointInsertionIndices

findBestWaypointInsertionIndices(
    route: Route,
    existingWaypoints: WaypointLike[],
    newWaypoints: WaypointLike[],
): number[]
The multi-waypoint variant of findBestWaypointInsertionIndex.

It projects every existing and new waypoint onto the route once, and gives each new waypoint the slot in existingWaypoints it falls in by its along-route location.
Parameters
- route: Route
  The existing calculated route, a Feature with LineString geometry.
- existingWaypoints: WaypointLike[]
  The existing waypoints in order, from origin through intermediate waypoints to destination.
- newWaypoints: WaypointLike[]
  The waypoints to find insertion slots for.
Returns number[]
The insertion slot indices, one per new waypoint, in input order.
Remarks
- Several new waypoints may share a slot. To merge them into the existing array in along-route order too, use withInsertedWaypoints, which ranks them within each slot.
- An empty newWaypoints returns an empty array.
- If the route has fewer than 2 coordinates or there are fewer than 2 existing waypoints, every new waypoint gets 0, so they would all prepend.